1. Field of the Invention
The present invention relates to a sensor to measure the angular position of a steering system. More particularly, the present invention relates to magnetostrictive linear displacement and other transducers for use with a steering wheel to measure the angular position of the steering wheel.
2. Background Art
Various devices have been advanced to measure the distance traveled by a device in a vehicle. One common application is determining the movement of the piston in a hydraulic, pneumatic, or hydro-pneumatic component of the vehicle, such as a strut suspension, where the piston moves axially in a cylinder filled with at least one damping medium. See U.S. Pat. Nos. 4,502,006; 4,638,670; and 5,233,293, each of which discloses a displacement sensor to perform this function.
Measuring the angle position of a car steering wheel is required for many purposes, such as traveling dynamic system, or for automatic electronic reset of a driving direction indicator after traveling through curves. An opto-electronically operating position sensing system for this steering angle determination is described in DE 40 22 837 A1. The steering angle sensing system described in DE 40 22 837 A1 consists of two elements arranged in parallel separated by a distancexe2x80x94a light source and a sensor linexe2x80x94as well as a code disk built as a transducer arranged between the light source and the sensor line, and coupled to the movement of the steering shaft. The light source and sensor line are stationary related to the transducer disk. The transducer disk is a light-slot disk and has, as a scanning track, a spiral with increasing diameter from the center towards the outer periphery. Dependent on steering angle movement, different pixels of the sensor line are lit by different areas of the scanning track. Dependent of which pixels or pixel clusters are lit in a defined steering wheel position, the steering angle is determined within a circle of 360xc2x0 or less, for example 270xc2x0, and requires counting revolutions beyond such amount.
The measuring accuracy of such an opto-electronic steering angle sensing system is determined by accuracy and fineness of the scanning tracks of the transducer disk and by projection sharpness of the light tracks on the photo-sensitive surface of the sensor line. If high accuracies are required, light-slot disks of very complicated structure must be provided. With this type of opto-electronic steering angle sensing system, there is also a risk of contamination of the very fine light slots and of the photo-sensitive surface of the sensor line so that steering angle measurement could be affected negatively.
An object of the present invention is to have a contactlessly operating steering angle sensing system for measuring the angle position of a car steering wheel, which is insensitive to contamination and does not require counting of the wheel revolutions to determine the absolute wheel position avoiding the problem in the prior art of regaining a lost count.
A vehicle steering angle sensing system is disclosed for detecting the angle position of an automotive steering wheel. It comprises a transducer coupled to the rotary movement of the steering wheel and a measuring device. The measuring device is stationary referred to the transducer rotary movement, for measurement of transducer signals. Thus, the measuring device and transducer are arranged so that the transducer signals detected by the measuring device represent the relative position between steering wheel and measuring device.
In the invention, the contactless operating steering angle sensing system couples at least one position magnet as a sensor of the rotary movement of the steering wheel, and by providing an elongated magnetostrictive waveguide extending over a defined arc sector with a mode converter mounted at one end of the waveguide forms a magnetostrictive transducer. The magnet field of the position magnet acts on different positions of the waveguide dependent upon the steering wheel position.
The signals generated from the position magnet in response to a pulse on the waveguide act on the waveguide when using such a device as a measure device. Steering angle measurement is obtained this way even in the presence of contamination of the detecting or measuring device.
Beside the primary rotary sensor which is capable of measuring an angle of 360xc2x0 or less, for example 270xc2x0, and is mounted to measure the steering wheel position, a secondary position sensor is used to measure the actual vehicle wheel steered position to provide an absolute multiple revolution sensing system that does not require counting of the revolutions of the steering wheel. The accuracy of the primary sensor is sufficient to provide the desired accuracy of data needed for steering function requirement, while the secondary sensor accuracy is only sufficient to indicate which revolution of the primary sensor is being measured.